The diagnosis and treatment of patients with cancerous tumors, pre-malignant conditions, and other disorders has long been an area of intense investigation. Non-invasive methods for examining tissue include: palpation, X-ray imaging, magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound imaging. When a physician suspects that tissue may contain cancerous cells, a biopsy may be done using either an open procedure or a percutaneous procedure. For an open procedure, a scalpel is used to create a large incision to provide direct visualization of and access to the tissue mass of interest. The entire mass (excisional biopsy) or a part of the mass (incisional biopsy) may then be removed. In percutaneous biopsy procedures, a needle-shaped instrument is inserted through a small incision to access the tissue mass of interest and obtain a tissue sample for later examination and analysis.
Aspiration and core sampling are two percutaneous methods for obtaining tissue from within the body. In an aspiration procedure, tissue is fragmented into pieces and drawn through a fine needle in a fluid medium. The aspiration method is less intrusive than most other sampling techniques, however, it has limited application since the structure of tissue excised by aspiration is destroyed, leaving only individual cells for analysis. In core biopsy, a core or fragment of tissue is obtained in a manner that preserves both the individual cell and the tissue structure for histological examination. The type of biopsy used depends on various factors, no single procedure is ideal for all cases.
A biopsy instrument now marketed under the tradename MAMMOTOME™ is commercially available from Ethicon Endo-Surgery, Inc. for use in obtaining breast biopsy samples, such as described in U.S. patent application No. 2003/0199753, published Oct. 23, 2003 to Hibner et al., which is hereby incorporated by reference in its entirety. The MAMMOTOME™ biopsy instrument is adapted to obtain multiple tissue samples from a patient with only one percutaneous insertion of a piercing element or piercer into the patient's breast. An operator uses the MAMMOTOME™ biopsy instrument to “actively” capture (using vacuum) tissue prior to severing it from surrounding tissue. Tissue is drawn into a lateral port at the distal end of the piercer by a remotely actuated vacuum system. Once the tissue is in the lateral port, a cutter is rotated and advanced through a lumen of the piercer past the lateral port. As the cutter advances past the lateral port opening, it severs the tissue in the port from the surrounding tissue. When the cutter retracts, it pulls the tissue with it and deposits the tissue sample outside of the patient's body.
This version of the MAMMOTOME™ core sampling biopsy instrument is advantageously compatible with use in a Magnetic Resonance Imaging (MRI) system. In particular, ferrous materials are avoided in the instrument so that the strong magnetic field of the MRI system does not attract the instrument. In addition, materials and circuitry are chosen to avoid artifacts in the MRI image by not interfering with the weak RF fields emanated by the tissue being examined. In particular, a control console that is remotely placed from the instrument provides the vacuum, cutter motor control, and graphical user interface. Thus, a flexible driveshaft couples the rotational motions for cutter translation and rotation.
While such an instrument provides a number of advantages for clinical diagnostic and therapeutic procedures in an MRI system, there are clinical applications wherein it is desirable to provide an MRI-compatible core sampling instrument that is not tethered, via a flexible driveshaft, to a control console. The driveshaft, although flexible, still imposes constraints due to its limited radius of bending. In addition, the drive shaft has an amount of inherent twist per length that creates a mechanical delay that may adversely impact closed-loop control, especially if a longer drive shaft is desired.
Another generally known approach to performing a core biopsy sampling is described in U.S. Pat. No. 6,758,824 wherein pneumatic pressure is used to turn a hydraulic rotary motor for cutter rotation and a hydraulic reciprocating actuator for cutter translation. While use of a remote pneumatic source connected through flexible pneumatic conduits is believed by some to be convenient and economical, such generally-known pneumatically-powered core biopsy systems do have some shortcomings.
An inherent issue with pneumatic drive motors is slow response time and inability to maintain a desired output shaft speed under loaded conditions. This phenomenon is associated with the compressibility of the gas that drives the system. In the case of a biopsy device containing a hollow cutter that rotates and translates, if dense tissue is encountered, the rotational speed of the pneumatically driven cutter may slow resulting in inconsistent tissue samples. And if the cutter is translated via a pneumatically driven piston-cylinder mechanism, the translation speed of the cutter may or may not change due to the density of the tissue. Therefore, the uncoordinated relationship between the cutter rotation speed and translation speed, coupled with the inherent poor response of the pneumatically driven cutter, often results in variations in the tissue sample weight when sampling heterogeneous tissue. It is believed that tissue sample weights are larger and more consistent when the number of rotations of the cutter through the aperture exceeds a minimum number of rotations.
Consequently, a significant need exists for a core biopsy device that is capable of use in proximity to an MRI machine as well as other imaging modalities yet avoids the inconveniences of being tethered by relatively long mechanical driveshafts as well as the inconsistent sample sizes produced by generally-known pneumatically-powered core sampling biopsy systems.